Preferential adsorption of Cu in a multi-metal mixture onto biogenic elemental selenium nanoparticles

Preferential adsorption of Cu contained in wastewaters is desirable as the Cu can then be reprocessed and reused more easily. In this study, biogenic elemental selenium nanoparticles (BioSeNPs) were assessed for their ability to preferentially adsorb Cu from an equimolar mixture containing Cu, Cd and Zn. Both metal to BioSeNPs ratio and initial metal solution pH have been shown to affect the preferential adsorption capacity of BioSeNPs towards Cu. BioSeNPs adsorbed 2.3 times more Cu from an equimolar mixture of Cu, Zn and Cd at an initial metal solution pH of 5.2 and metal to BioSeNPs ratio of 0.21 mg mg−1, while adsorbing more than 78% of added Cu. Infrared spectroscopy revealed that the Cu, Cd and Zn were interacting with hydroxyl and carboxyl surface functional groups of the BioSeNPs. The modeling of BioSeNPs' acid-base titration revealed the presence of high concentrations of carboxylic groups (C = 60.26 mol Kg−1) with a pKa of 3.9 providing, further evidence of their interaction with Cu. The adsorption of Cu resulted in a lower colloidal stability of the BioSeNPs as indicated by less negative ζ-potential values. BioSeNPs showed good preferential adsorption capacity towards Cu when compared to oxidized carbon nanotubes. This study provides proof-of-concept for preferential adsorption of Cu onto BioSeNPs which are present in the effluent of a bioreactor treating selenium oxyanions containing wastewater.